Device for the protection of an electrical load and power supply circuit having such a device

Abstract

Device for the protection of an electrical load. A branch (4) connects an input terminal (1) to an output terminal (2). The branch includes in series: a channel of a first transistor (10) of the "normally on" type and a channel of a second transistor (20) of the "normally on" type of a second conductivity type. A gate (10g) of the first transistor (10) is connected to the output terminal (2) and a gate (20g) of the second transistor (20) is connected to the input terminal (1) by means of a third "normally on" transistor (30) of the first conductivity type. A gate (30g) is connected to a node (6) between the channels of the first and second transistors. The device has application to the protection of electronic components.

What is claimed is: 
     
       1. Device for the protection of an electrical load, comprising a conduction branch (4) connecting an input terminal (1) to an output terminal (2), the conduction branch having in series: a channel of a first transistor (10) of the "normally on" type polarized to be switched between conductive and inhibited states, of a first conductivity type, and   a channel of a second transistor (20) of the "normally on" type polarized to be switched between conductive and inhibited states of a second conductivity type, opposite to the first conductivity type, and wherein a gate (10g) of said first transistor (10) is connected to the output terminal (2), and a gate (20g) of the second transistor (20) is connected to the input terminal (1) by means of a third transistor (30) of the "normally on" type and of the first conductivity type, the third transistor having a gate (30g) connected to a node (6) located between the channels of the first and second transistors.   
     
     
       2. Device according to claim 1, also having a reverse-biased Zener diode (8) connecting the gate of the second transistor (26) to the output terminal (2). 
     
     
       3. Device according to claim 1, wherein the first, second and third transistors respectively have first, second and third threshold voltages (V T10 , V T20 , V T30 ), chosen in such a way that the third transistor (30) remains in the on state whilst a current flows through the first and second transistors. 
     
     
       4. Device according to claim 3, wherein the threshold voltage of the third transistor is chosen in such a way that the third transistor is inhibited when the voltage applied between the input and output terminals is higher than the voltage for damaging the gate of the second transistor. 
     
     
       5. Device according to claim 3, wherein the threshold voltages of the first and second transistors (10, 20) are of opposite signs, substantially equal in absolute value and lower in absolute value than the threshold voltage of the third transistor (30). 
     
     
       6. Device according to claim 1, wherein the first and third transistors are transistors of the "high voltage" type. 
     
     
       7. Device according to claim 1, wherein the first and third transistors are transistors of the IGBT type and the second transistor is of the MOS type. 
     
     
       8. Device according to claim 1, wherein the first, second and third transistors are MOS transistors. 
     
     
       9. Device according to claim 1, wherein the input terminal is a positive terminal, in which the first and third transistors are of the N-type and in which the second transistor is of the P-type. 
     
     
       10. Device according to claim 1, implemented in the form of an integrated circuit. 
     
     
       11. Power supply circuit of an electrical load comprising an electrical load (112) in series with a protection device (100), characterized in that the protection device (100) is in accordance with claim 1.